Who were the Khmer Rouge?

Up to two million people thought to have died of starvation, overwork or by execution

Defeated in Vietnamese invasion in 1979

Pol Pot fled and remained free until 1997 - he died a year later

But medical experts declared her unfit to stand trial, and her release was ordered.

However, the tribunal ruled late on Tuesday: "The supreme court chamber concluded that the original ground for keeping the accused in provisional detention, namely to ensure her presence during the proceedings, remains valid and relevant."

The judges added that she would be transferred to medical facility for treatment "which may help improve her mental health to such an extent that she becomes fit to stand trial".

The other leaders on trial are Pol Pot's deputy, Nuon Chea, and Khieu Samphan, the regime's former head of state.

All three deny the charges they face.

The UN-backed court's first case was the trial of Duch, the former Khmer Rouge prison chief who oversaw the torture and execution of thousands of inmates at Tuol Sleng prison.